Autodesk AUTOCAD 2006, Command Reference Manual, Page: 1132 / 1490

Height of Extrusion
Sets the direction and height of the extrusion. Entering a positive value
extrudes the face in the direction of its normal. Entering a negative value
extrudes the face in the direction opposite to its normal.
Specify angle of taper for extrusion <0>: Specify an angle between –90 and +90
degrees or press ENTER
positive angle
extruded face
negative angle
extruded face
face selected
Tapering the selected face with a positive angle tapers the face in, and a
negative angle tapers the face out. The default angle, 0, extrudes the face
perpendicular to its plane. All selected faces in the selection set are tapered
to the same value. If you specify a large taper angle or height, you can cause
the face to taper to a point before it reaches the extrusion height.
Path
Sets a path for the extrusion path based on a specified line or curve. All the
profiles of the selected face are extruded along the chosen path to create
the extrusion.
Select extrusion path: Use an object selection method
1108 | Chapter 20